Epidemiology

Indigenous hepatitis E virus on the rise in England and Wales

Last Updated: 2013-12-27 15:23:51 -0500 (Reuters Health)

By Will Boggs MD

NEW YORK (Reuters Health) - A new group of genotype 3 hepatitis E viruses (HEV) accounts for the sudden rise in indigenously acquired cases in England and Wales since 2010, researchers report.

"The data from our study suggests that we are currently in a period of heightened HEV activity in England and Wales," Dr. Samreen Ijaz from Public Health England in London told Reuters Health by email. "The last three years have seen a year on year increase in case numbers and the emergence of a group of viruses not commonly circulating in England and Wales prior to 2010."

Usually asymptomatic, HEV has infected an estimated 13% of the population in England, with an annual rate of 0.1% to 0.2% and an estimated 60,000 infections per year, Dr. Ijaz and colleagues report in The Journal of Infectious Diseases, online November 23.

HEV antibodies and viral RNA have been reported in various farm and domestic animals, and there is close sequence homology between human HEV strains and HEV sequences isolated from boar, deer, and pigs. What accounts for the HEV infection acquired in England, however, remains unclear.

Dr. Ijaz and colleagues used HEV antibody and RNA data from England and Wales to ascertain the annual number of acute infections, the HEV genotype disposition and viral phylogeny over the past decade.

Of the 2,713 acute cases between January 2003 and December 2012, 51% appeared to be indigenous infections, based on reported absence of travel history or Caucasian name as a proxy.

The annual number of cases followed an erratic course between 2005 and 2009 before increasing sharply from 2010 (n=274) to 2011 (n=456) and 2012 (n=579), the highest incidence on record.

The proportion of indigenously acquired HEV cases reached 71% in 2012, whereas the case numbers for travel-associated HEV remained relatively stable between 100-200 infections per year during 2010-2012, the researchers report.

Most cases related to travel abroad were genotype 1 infections, which arose mainly from exposure on the Indian subcontinent.

The majority of indigenous cases, on the other hand, were genotype 3 viruses from two major phylogenetic groups. Most cases from 2003-2009 clustered in group 1, whereas most cases from 2010-2012 clustered in group 2.

The team says this indicates "the possibility of two parallel zoonoses but sequential epidemics currently occurring in England and Wales."

Phylogenetic analysis also found that sequences from UK pigs collected in 2004, 2005, and 2008 clustered within genotype 3 group 1.

"Hepatitis E has recently emerged as the most common cause of acute viral hepatitis in England and Wales," the researchers note. "This increase in diagnosis may partly be explained by the historical problems over the laboratory diagnosis of hepatitis E with ascertainment over the study period improved by the introduction in both reference laboratories of new commercially available antibody detection assays with improved sensitivity and importantly specificity."

The testing approach did not change between 2010 and 2012, though.

"The observed fluctuation in the risk of acquiring HEV is not without precedent," Dr. Ijaz said. "Similar indications of changes in the historical risk of HEV acquisition were revealed by population-based English seroprevalence data generated for two time points of 1991 and 2004. A pronounced cohort effect indicated a greater risk of HEV infection during the post second world war decade. The evidence suggests that the risk of acquiring HEV fluctuates, but what leads to alterations in risk remains unclear."

"From a public health perspective our data highlights the need to better understand the routes of transmission in this country and also what has led to a change in the magnitude of the risk of acquiring HEV," Dr. Ijaz said. "We can speculate that factors such as changes in farming practices, animal husbandry, the handling and processing of food, or indeed the importation of meat could have resulted in a change in risk."

"What we do know from studies yet to be published is that there are very many more infections in England than there are cases of hepatitis E and that most HEV infections are asymptomatic," Dr. Ijaz said. "There are concerns about the risk of immunosuppressed persons developing persistent infections and about transmission by blood transfusion."

"We are unaware of similar surveillance programs from other countries," Dr. Ijaz added. "However, informal discussions with colleagues working on hepatitis E in Europe have suggested a recent increase in case numbers from within their populations but these data have not been formally published and made available. In particular our colleagues in the Dutch transfusion service have shown a high seroconversion rate in younger donors indicating similar widespread infection in that country."

SOURCE: http://bit.ly/1cTQ5mo

J Infect Dis 2013.